A person's circulatory system includes both systemic and pulmonary circulation. Pulmonary circulation supplies the lungs with blood flow, while the systemic circulation takes care of all the other parts of the body. The heart serves as a pump that circulates the blood, while blood vessels act as the conduits that deliver blood to tissue. During systole, that is, during ventricular contraction, blood pressure in the aorta and pulmonary artery rises until their valves close after which the pressure pulse declines to a rather steady state during diastole. A cardiac cycle begins with initiation of the QRS complex in the electrocardiogram or intracardiac electrogram (ECG or IEGM) waveform. It takes a certain amount of time for a heart stimulus signal to propagate and to effect depolarization of the ventricular tissue cells so there is a short delay before ventricular contraction starts. The time elapsed between the beginning of the QRS complex and the onset of ventricular contraction can be defined as the pre-ejection interval (PEI).
PEI has been shown to be an important parameter to assess cardiac functionality. For example, an increase in PEI indicates worsened heart failure condition while a shorter PEI indicates an improved heart failure condition. One approach used to obtain a measurement of PEI involves using Echo measurements. However, such an approach typically is costly and time-consuming. Additionally, obtaining a measurement of PEI using Echo-based measurements makes it difficult to measure PEIs continuously.
Accordingly, it would be beneficial to provide less costly and time consuming measures of for monitoring PEI.